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What Causes 24 Hours of Light?

The idea of a land where the sun never sets has long captivated poets and photographers. Because most inhabited parts of Earth don't ever experience 24 hours of daylight--what's known as a midnight sun--some travelers take cruises and other journeys just to experience the feeling of sunlight in the middle of the night, which occurs near Earth's poles around the summer and winter solstices.

Tilt of the Axis
- Rather than standing straight up and down, Earth's axis tilts at a 23.5 degree angle. This slight inclination means that at certain times during Earth's 365-day orbit around the sun each year, the northernmost and southernmost portions of the planet will be either inclined toward or inclined away from the sun, which dramatically affects the amount of sunlight they receive every day.
Northern Hemisphere
- The North Pole inclines toward the sun around the time of the solstice that occurs on June 21. Areas north of the Arctic Circle will experience light 24 hours a day, since the sun will never disappear below the horizon. The farther north you go, the longer the sun remains continuously above the horizon. Qaanaaq, toward the northern part of Greenland, experiences continuous sunlight from mid-April to late August of each year, according to the Greenland.com website.
Southern Hemisphere
- In the Southern Hemisphere, the situation is reversed. Around the South Pole, 24-hour sunlight occurs around the December 21 solstice, because that is when Earth's axis tilts to point the South Pole toward the sun and the North Pole away from the sun. While the South Pole is experiencing continuous sunlight around December 21, the North Pole is experiencing the opposite: continuous darkness.
Adaptation
- Plants and animals that live near the North and South Poles must find ways to adapt to these unusual extremes of daylight and temperature that occur throughout the year. Adaptive strategies include migration away from the poles, periods of dormancy or hibernation during the dark times, and periods of significant growth and development during the light times.

Nature